Assessment of the impact of pore-scale mass-transfer restrictions on microbially-induced stable-isotope fractionation |
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| Institution: | 1. Dpto. Ingeniería de Alimentos y del Equipamiento Agrícola, Campus de Excelencia Internacional Regional “Campus Mare Nostrum”, Universidad Politécnica de Cartagena, Paseo Alfonso XIII, 48, 30203 Cartagena, Spain;1. Department of Watershed Management Engineering, Faculty of Natural Resources, Tarbiat Modares University, Noor 46417-76489, Iran;2. Department of Desert Regions Management, College of Agriculture, Shiraz University, Iran |
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| Abstract: | Stable-isotope fractionation has become an established method for the assessment of contaminant biodegradation in groundwater. At the pore scale however, mass-transfer processes can limit the bioavailability of chemical species and therefore affect the observed fractionation. This can challenge the application of stable-isotope analysis in practice. A linear-exchange model provides a computational link between the microbially-induced isotope fractionation, determined under ideal conditions, and the fractionation observed under conditions of limited bioavailability. This simplifying conceptual approach allows for accurately estimating the mass-transfer limited degradation rates but its applicability for stable-isotope fractionation at the pore scale has not been evaluated yet. In this study, we perform high-resolution numerical simulations of microbial degradation and stable-isotope fractionation of a chemical species in a pore-scale model. The numerical results are compared to theoretical predictions derived from the linear-exchange model. Our results show an overall good agreement between numerical simulations and theoretical predictions, which confirms the applicability of the theoretical approach and of the value for the mass-transfer coefficient previously derived from the geometry of the pore space. In addition we provide a quantitative link between the value of the observable fractionation factor and the effective bioavailability of a biodegradable contaminant. |
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| Keywords: | Compound-specific stable-isotope analysis CSIA Bioavailability Numerical modeling Linear-exchange model Michaelis–Menten kinetics |
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